Phase detector

ABSTRACT

Disclosed is a phase detection apparatus for accurately calculating the phase of an input digital complex baseband signal point independently of its amplitude value, without requiring any large-capacity arc-tangent table memory and within a practical calculation time. This phase detection apparatus rotates the phase of the input signal point in a clockwise direction and determines whether the rotated signal point agrees with a reference phase point. If the rotated signal point leads the reference phase point, the signal point is further rotated by an angle onehalf of the predetermined angle. If the rotated signal point lags behind the reference phase point, the signal point before the rotation is rotated by a half angle of the predetermined angle. Rotational angles, 180°, 90°, 45°, . . . , for the individual rotations are stored in a table. If the rotated signal point agrees with the reference phase point after the rotation processing is performed several times, or, even if the two points do not agree, if all of the rotational angles stored in the table are used in the rotation processing, the sum of the angles rotated so far is output as the phase of the input signal.

TECHNICAL FIELD

The present invention relates to a phase detection apparatus used todetect the phase of a received signal in a carrier wave reproductioncircuit for synchronous detection, a phase detection circuit, or afrequency detection circuit provided in, e.g., a digital mobile radiocommunication apparatus or a satellite communication apparatus.

BACKGROUND ART

Recently, with the development of semiconductor technologies,particularly digital IC technologies, a digital demodulation circuit isin many instances realized by a digital signal processing circuit in aradio communication apparatus for use in a digital cellular radiocommunication system or a satellite communication system. In a digitaldemodulation circuit of this type, a quadrature detector detects, e.g.,a received radio signal and converts the signal into a complex basebandsignal. An A/D converter converts this complex baseband signal into adigital complex baseband signal. A digital signal processing circuitperforms synchronous detection, phase detection, or frequency detectionfor this digital complex baseband signal.

To realize the digital demodulation function as described above, it isnecessary to detect the phase from the received complex baseband signal.The following various apparatuses have been developed as conventionalphase detection apparatuses for performing this phase detection.

(1) A phase is the arc tangent (tan⁻¹ (Q/I)) of a real-part component Iand an imaginary-part component Q of a digital complex baseband signal.Accordingly, calculate the arc tangents of combinations of various I andQ values in advance, and prepare a table in a ROM. Input I and Q asaddresses to the ROM, and output a phase corresponding to these inputaddresses from the table.

(2) Instead of calculating arc tangents in advance, calculate them bymeans of series expansion.

(3) Regard the value of the imaginary-part component Q as a phase.

(4) Calculate Q×sign(I), and regard the calculated value as a phase.Note that sign(X) is +1 when the sign of X is positive, and -1 when thesign is negative.

(5) Calculate Q×sign(I)-I×sign(Q), and regard the calculated value as aphase.

These conventional phase detection apparatuses have the followingproblems.

That is, system (1) using a table ROM requires a large-capacity ROM.This increases the circuit scale of the apparatus, leading to thedifficulty in decreasing the size and weight of the apparatus. Thisdegrades the portability of mobile communication apparatuses such asportable telephone sets whose most important objectives are a small sizeand a light weight. Therefore, system (1) is very undesirable in theseapparatuses.

In system (2), calculations must be repetitively done a large number oftimes. Since this prolongs the calculation time, system (2) isunsuitable for real-time processing of communication apparatuses.

Systems (3) to (5) have the advantage that only relatively simplecalculations need to be performed in these systems. However, thesesystems can detect only the polarity of the phase or the magnitude ofthe signal level, i.e., cannot detect the phase itself. In particular,because of variations in the calculation results these systems cannotcalculate an accurate phase from a signal, such as a received signalmodulated by a π/4 shift DQPSK system, which changes its amplitude levelin accordance with the phase position.

The present invention has been made in consideration of the abovesituation and has its object to provide a phase detection apparatuswhich requires no large-capacity memory and can calculate an accuratephase, within a practical calculation time, independently of theamplitude value of an input signal.

It is another object of the present invention to provide a phasedetection apparatus suited for use in mobile communication apparatuses.

DISCLOSURE OF INVENTION

To achieve the above objects, a phase detection apparatus of the presentinvention comprises phase rotating means for rotating a phase of aninput signal point, rotational angle setting means for supplying aplurality of rotational angles in decreasing order to the phase rotatingmeans, phase comparing means for determining whether the signal pointrotated by the phase rotating means agrees with a reference phase pointwithin a predetermined error range, control means for sequentiallyrotating the phase of the input signal point by the plurality ofrotational angles, until the phase comparing means detects theagreement, or, even if the phase comparing means does not detect theagreement, until the rotational angle setting means supplies all of theplurality of rotational angles to the phase rotating means. The controlmans output data indicating the phase of the input signal point based ona sum of the phase rotational angles.

As a consequence, the phase detection apparatus of the present inventioncan perform phase detection without using any large-capacity memory.Accordingly, the circuit scale can be decreased compared to the casewhere an arc-tangent ROM is used. This makes it possible to realizereductions in the size and weight of, e.g., a mobile radio communicationapparatus.

Also, since the phase rotation is done in decreasing order of angle, thephase of an input signal can be made agree with the reference phase by arelatively small number of repetition times. This obviates the need fora large number of repetitive calculations, making phase detection inshort time periods feasible.

Furthermore, the detection system is independent of the amplitude valueof an input signal. Consequently, accurate phase detection can beperformed even in processing a signal, such as a received signalmodulated by a π/4 shift DQPSK system, which changes its amplitude levelin accordance with the phase position.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the configuration of a receivingsystem of a mobile radio communication apparatus which includes a phasedetection apparatus according to the first embodiment of the presentinvention;

FIG. 2 is a view showing an example of a sin/cos data table illustratedin FIG. 1;

FIG. 3 is a flow chart showing the operation of the first embodiment;

FIG. 4 is a view showing the way of phase rotation to explain theoperation of the first embodiment;

FIG. 5 is a view showing an example of a sin/cos data table used in aphase detection apparatus according to the second embodiment of thepresent invention;

FIG. 6 is a flow chart showing the major steps of the operation of thesecond embodiment;

FIG. 7 is a view showing the way of phase rotation to explain theoperation of the second embodiment;

FIG. 8 is a block diagram showing the configuration of a receivingsystem of a mobile radio communication apparatus which includes a phasedetection apparatus according to the third embodiment of the presentinvention;

FIG. 9 is a flow chart showing the operation of the third embodiment;and

FIG. 10 is a view showing the way of phase rotation to explain theoperation of the third embodiment.

BEST MODE OF CARRYING OUT THE INVENTION

To describe the present invention in more detail, its embodiments willbe described below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of a receivingsystem of a mobile radio communication apparatus which includes a phasedetection apparatus according to the first embodiment of the presentinvention.

Referring to FIG. 1, a radio frequency signal coming from a base station(not shown) is received by an antenna 11, amplified by a low-noiseamplifier 12, and applied to a quadrature detection circuit 13. In thequadrature detection circuit 13, the received radio frequency signal isfirst divided into two signal components and applied to mixers 14I and14Q. The mixers 14I and 14Q mix the respective signal components withreception local oscillation signals having a π/2 phase difference.Consequently, these signal components are frequency-converted into areal-part (I) component and an imaginary-part (Q) component of a complexbaseband signal. A local oscillation signal generated by a frequencysynthesizer 16 is directly supplied to the mixer 14I and supplied to themixer 14Q via a π/2 phase shifter 15. The output I and Q components ofthe received complex baseband signal from the mixers 14I and 14Q arefiltered by baseband filters (low-pass filters) 17I and 17Q and appliedto A/D converters (ADCs) 18I and 18Q. The A/D converters 18I and 18Qconvert the input signals into digital signals and transfer them to thephase detection apparatus.

The phase detection apparatus comprises a first latch circuit 21 and asecond latch circuit 22 for receiving the digital complex basebandsignals (I and Q components), a selector 23 for selecting one of outputsfrom the first and second latch circuits 21 and 22 and also supplyingthe output to the second latch circuit 22, a phase rotation circuit 24for rotating the phase of the output signal from the selector 23 andalso supplying the output to the first latch circuit, a sin/cos datatable 25 for giving phase rotational angle information to the phaserotation circuit 24, a fixed value storage circuit 27, a comparator 26for comparing the phase of the output signal from the phase rotationcircuit 24 with the output from the fixed value storage circuit 27, astorage circuit 28 for storing the output from the comparator 26, and acontrol circuit 29. Note that in the block diagram of the phasedetection apparatus, the I and Q components of the digital complexbaseband signal are together indicated by thick lines.

The A/D converters 18I and 18Q output the digital complex basebandsignals (a unit of the digital signal periodically output from the A/Dconverter will be referred to as a sample hereinafter) at apredetermined period corresponding to a sampling clock, and the phase ofeach sample is detected. Before the sample phase detection operation isstarted, the first latch circuit 21 holds the output digital complexbaseband signals from the A/D converters 18I and 18Q. After the phasedetection operation is started, the first latch circuit 21 holds theoutput phase-rotated digital complex baseband signal from the phaserotation circuit 24. On the other hand, the second latch circuit 22holds the digital complex baseband signal before phase rotation, whichis supplied to the phase rotation circuit 24, each time the phaserotation circuit 24 performs phase rotation. The signal holding andreading operations by these first and second latch circuits 21 and 22are done in accordance with instructions from the control circuit 29.

The selector 23 which consists of, e.g., a multiplexer alternativelyselects the phase-rotated complex baseband signal held by the firstlatch circuit 21 and the complex baseband signal before phase rotationheld by the second latch circuit 22, in accordance with instructionsfrom the control circuit 29, and supplies the selected signal to thephase rotation circuit 24.

The phase rotation circuit 24 rotates the phase of the complex basebandsignal supplied from the selector 23 by an angle corresponding to sindata and cos data supplied from the sin/cos data table 25. The phaserotation circuit 24 outputs the resulting phase-rotated complex basebandsignal.

Assuming the input to the phase rotation circuit 24 is I+jQ, a signal I'+jQ' after the rotation is represented by

    I'=I·cos θ-Q·sin θ

    Q'=Q·cos θ+I·sin θ

where θ is positive in the clockwise direction.

The sin/cos data table 25 comprises a ROM in which, as illustrated inFIG. 2, sin data and cos data representing a rotational angle of360°/2^(n) (n=1 to 8), that is, eight rotational angles of 180°, 90°,45°, 22.5°, 11.3°, 5.6°, 2.8°, and 1.4°, are stored in a one-to-onecorrespondence with addresses 1 to 8. These sin and cos data areselectively read out in accordance with an address supplied from thecontrol circuit 29. Note that the rotating direction of the phaserotation circuit 24 is fixed in the clockwise direction.

The comparator 26 compares the phase of the output phase-rotated complexbaseband signal from the phase rotation circuit 24 with the referencephase previously stored in the fixed value storage circuit 27, therebydetermining whether the phase of the complex baseband signal leads, lagsbehind, or agrees with the reference phase signal. The comparator 26outputs a signal of level "1" if it determines that the phase of thesignal leads the reference phase, a signal of level "-1" if itdetermines that the phase of the signal lags behind the referencesignal, and a signal of level "0" if it determines that the phase of thesignal agrees with the reference phase. These determination signals areinput to the control circuit 29. Note that 0°, for example, is used asthe reference phase. In this determination by the comparator 29, thedetermination of whether the phase of the complex baseband signal agreeswith the reference phase need not be done by determining whether thephase of the signal completely agrees with the reference phase. That is,the agreement can be determined if the phase of the signal falls withina certain allowable error range with respect to the reference signal.

The control circuit 29 controls the whole phase detection operation doneby the individual circuits described above. That is, in accordance withthe output determination signal from the comparator 26, the controlcircuit 29 controls the selector 23 to selectively supply the complexbaseband signals held in the first and second latch circuits 21 and 22.Also, in synchronism with this control the control circuit 29 reads outthe sin and cos data, which represent the phase rotational angle, indecreasing order of angle from the sin/cos data table 25, and suppliesthe readout data to the phase rotation circuit 24, thereby making thephase rotation circuit 24 rotate the phase of the complex basebandsignal. Furthermore, the control circuit 29 writes a value correspondingto the determination result from the comparator 26 into the storagecircuit 28. The storage circuit 28 comprises, e.g., a RAM.

The operation of the phase detection apparatus with the abovearrangement will be described below with reference to the flow chart ofthe control circuit 29 shown in FIG. 3. The gist of the operation of thepresent invention is as follows. That is, when the sample signal pointof a digital complex baseband signal is supplied, the control circuit 29rotates the sample point on a phase plane in sequence by the individualrotational angles registered in the table shown in FIG. 2 whiledetermining whether the phase of each rotated signal point agrees withthe reference phase. If the agreement is detected, the control circuit29 detects the sum of the angles rotated so far as the phase angle ofthe sample point.

When the operation is started, initialization is performed as in step#10, i.e., 0 is set in a parameter i which represents the number ofrotations.

When the A/D converters 18I and 18Q output digital complex basebandsignals of one sample, in step #12, the first latch circuit 21 latchesthe data of one sample point.

In step #14, the selector 23 is controlled to select the first latchcircuit 21, and the sample point of the output digital complex basebandsignal from the quadrature detection circuit 13, which is held in thefirst latch circuit 21, is supplied to the phase rotation circuit 24.

In step #16, the control circuit 29 increments the parameter i by 1.

In step #18, the control circuit 29 supplies the parameter i as anaddress to the sin/cos data table 25, reads out sin data and cos datastored in that address, and supplies the readout data to the phaserotation circuit 24. That is, the control circuit 29 first designatesaddress 1 and reads out sin data and cos data corresponding to thelargest phase rotational angle, i.e., 180°.

In step #20, the phase rotation circuit 24 performs a phase shiftoperation by which the sample point of the digital complex basebandsignal, which is supplied via the selector 23 and held in the firstlatch circuit 21, is rotated clockwise.

In step #22, the control circuit 29 causes the first latch circuit 21 tolatch the data of the rotated sample point and the second latch circuit22 to latch the data of the sample point before the rotation.

In step #24, the control circuit 29 determines whether the parameter 1has reached 8. If YES in step #24, the control circuit 29 terminates theoperation since the phase rotation circuit 24 has completed the rotationprocessing for all of the rotational angles stored in the sin/cos datatable 25. If NO in step #24, in step #26 the comparator 26 determineswhether the phase of the rotated signal point agrees with a fixed valuecorresponding to the reference phase stored in the fixed value storagecircuit 27. If YES in step #26, the control circuit 29 stores "1" in thestorage circuit 28 in step #28 and ends the operation.

If NO in step #26, in step #30 the control circuit 29 determines whetherthe phase of the rotated signal point leads the reference phase (thephase of the rotated signal point is present before the reference pointin the counterclockwise direction). If YES in step #30, "1" is stored inthe storage circuit 28 in step #32. In step #34, the selector 23 iscontrolled to select the first latch circuit 21 for the next rotationprocessing, and the rotated phase is supplied to the phase rotationcircuit 24. Thereafter, the flow returns to step #16 to repeat the aboveoperation by incrementing the parameter i by 1. That is, the phase ofthe rotated signal point is further rotated by a half of the immediatelypreceding rotational angle. If the phase of the rotated signal pointlags behind the reference phase, "0" is stored in the storage circuit 28in step #36. In step #38, the selector 23 is controlled to select thesecond latch circuit 22 for the next rotation processing, and the phaseof the unrotated signal point is supplied to the phase rotation circuit24. Thereafter, the flow returns to step #16 to repeat the aboveoperation by incrementing the parameter i by 1. That is, the phase ofthe unrotated signal point is rotated by a half of the immediatelypreceding rotational angle.

A practical example of the operation of this embodiment will bedescribed below with reference to FIG. 4. Assume that the sample pointof a digital complex baseband signal is a point A in FIG. 4. This samplepoint A is first rotated by 180° in a clockwise direction to move to apoint B by the phase rotation circuit 24 (step #20).

As shown in step #14, the selector 13 selects the first latch circuit21. In step #22, therefore, the phase of the complex baseband signal atthe initial signal point A before the phase rotation held in the firstlatch circuit 21 is transferred to and held in the second latch circuit22 via the selector 23, and the output phase-rotated signal point B fromthe phase rotation circuit 24 is newly held in the first latch circuit21.

This phase-rotated signal point B is input to the comparator 26. Thecomparator 26 compares the phase of the input phase-rotated signal pointB with the reference phase, 0°, stored in the fixed value storagecircuit 27 (steps #26 and #30). The comparator 26 outputs a signal oflevel "1" if the phase of the signal point B leads the reference phase,a signal of level "-1" if the phase of the signal point B lags behindthe reference phase, and a signal of level "0" if the two phases agree.As shown in FIG. 4, in this case the phase of the phase-rotated signalpoint B leads the reference phase. Accordingly, the comparator 26outputs a signal of level "1". The control circuit 29 writes data "1" inthe storage circuit 28 as in step #32.

When the first phase rotation control is completed and the datacorresponding to the determination result is stored in the storagecircuit 28, the control circuit 29 performs the second phase rotationcontrol. On the basis of the determination result from the comparator26, the control circuit 29 selects a signal point to be subjected to thephase rotation next. In this case the determination signal is a signalof level "1" which indicates that the phase of the phase-rotated signalpoint has not reached (leads) the reference point. Accordingly, thecontrol circuit 29 determines that the phase rotational angle is stillinsufficient, and controls the selector 23 to select the first latchcircuit 21 which holds the phase-rotated signal point B (step #34).Consequently, the phase of the phase-rotated signal point B held in thefirst latch circuit 21 is supplied to the phase rotation circuit 24through the selector 23.

Thereafter, in step #18 the control circuit 29 performs addressdesignation for the second time to the sin/cos data table 25. As aresult, sin data and cos data corresponding to the second largest phaserotational angle, 90°, stored in address 2 are read out and supplied tothe phase rotation circuit 24. The phase rotation circuit 24 rotates thephase of the signal B by 90°. The resulting phase-rotated signal pointis a point C in FIG. 4.

Since the phase of this phase-rotated signal point C lags behind thereference phase (the phase is rotated too much), the comparator 26outputs a signal of level "-1". As shown in step #36, the controlcircuit 29 writes data "0" in the storage circuit 28. In step #38, thecontrol circuit 29 causes the selector 23 to select the second latchcircuit 22. Selecting the second latch circuit 22 means that the nextphase rotation processing is again performed for the current signalpoint before phase rotation. That is, in the third phase rotationprocessing, the signal point B before phase rotation held in the secondlatch circuit 22 is supplied to the phase rotation circuit 24 via theselector 23.

The control circuit 29 performs address designation for the third timeto the sin/cos data table 25. Consequently, sin and cos datacorresponding to a phase rotational angle of 45° stored in address 3 areread out from the sin/cos data table 25 and supplied to the phaserotation circuit 24. The phase rotation circuit 24 rotates the phase ofthe signal point B by 45°. This phase-rotated signal point is a point Din FIG. 4.

In step #22, in the same way as in the rotation processing for thefirst, second, and third times, the phase-rotated signal point D is fedback to and held in the first latch circuit 21, and the signal point Bbefore phase rotation held in the second latch circuit 22 is again fedback and held via the selector 23.

When the phase-rotated signal point D is output, the comparator 26compares the signal point D with a reference phase point F. Since thephase of the signal point D leads the phase of the reference phase pointF, the comparator 26 outputs a determination signal of level "1", anddata "1" is stored in the storage circuit 28.

When the third phase rotation control is completed and the datacorresponding to the determination result is stored in the storagecircuit 28, the control circuit 29 subsequently executes phase rotationcontrol for the fourth time. That is, on the basis of the outputdetermination signal of level "1" from the comparator 26, the controlcircuit 29 determines that the phase rotation in the third phaserotation control is still insufficient. Therefore, to select thephase-rotated signal point D, in step #34 the control circuit 29controls the selector 23 to select the first latch circuit 21.Accordingly, the phase-rotated signal point D held in the first latchcircuit 21 is supplied to the phase rotation circuit 24 through theselector 23.

The control circuit 29 then performs address designation for the fourthtime to the sin/cos data table 25. Consequently, sin and cos datacorresponding to a phase rotational angle of 22.5° are read out from thesin/cos data table 25 and supplied to the phase rotation circuit 24. Thephase rotation circuit 24 rotates the phase of the signal point D by22.5°. This phase-rotated signal point is a point E in FIG. 4. Thephase-rotated signal point E is fed back to and held in the first latchcircuit 21. Note that the signal point D before phase rotation which hasbeen held in the first latch circuit 21 is transferred to and held inthe second latch circuit 22.

When the phase-rotated signal point E is output, the comparator 26compares the signal point E with the reference phase point F. Since thesignal point E agrees with the reference phase point F, the comparator26 outputs a signal of level "0". Accordingly, in step #28 data "1" isstored in the storage circuit 28, and the control circuit 29 terminatesthe operation by determining that the phase of the sample A of thedigital complex baseband signal is detected.

If the rotated signal point does not agree with the reference phasepoint, the above operation is again repeated. However, when the rotationprocessing is performed for all the rotational angles stored in thesin/cos data table 25, the operation is ended as shown in step #24regardless of whether the phase agreement is attained. If this is thecase, an error of a minimum rotational angle of 1.4° or smaller isallowed.

When the operation is ended, the control circuit 29 reads out the data,"1011" in the case of FIG. 4, from the storage circuit 28, and suppliesthis value to a circuit (not shown) as phase detection data. Note that"1011" represents 11 in decimal notation and corresponds to360°×11/16=247.5° when a phase of 0° to 360° is represented by fourbits.

As described above, in this embodiment sin data and cos datarepresenting rotational angles of 180°, 90°, 45°, . . . are read out indecreasing order of angle from the sin/cos data table 25, and the phaserotation circuit 24 rotates the phase of a complex baseband signal.Thereafter, the comparator 26 compares the phase-rotated signal pointwith the reference phase point of phase 0°. On the basis of thedetermination result from the comparator 26, the selector 23alternatively selects the signal point before or after the phaserotation and supplies the selected signal point to the phase rotationcircuit 24 for the next phase rotation. This operation is repetitivelyperformed until the comparator 26 determines that the phase-rotatedsignal point agrees with the reference phase point or until all thephase rotational angles are read out from the sin/cos data table 25.

Accordingly, the sin/cos data table 25 need only store sin data and cosdata representing rotational angles of 180°, 90°, 45°, . . . that aresequentially reduced by one-half, so the phase detection can beperformed without using any large-capacity memory. Consequently, thecircuit scale can be decreased compared to the case where an arc-tangentROM is used. This makes it possible to decrease the size and weight of,e.g., a mobile radio communication apparatus.

Also, in this embodiment sin data and cos data representing rotationalangles of 180°, 90°, 45°, . . . are stored in the sin/cos data table 25.Therefore, these sin and cos data can be read out and directly used inthe phase rotation calculation. As an example, if data representingangles are stored as phase rotational angles, a table for converting theangle data into sin data and cos data is necessary. However, in thisembodiment no such table is necessary, and this further simplifies andminiaturizes the circuit configuration.

Furthermore, in this embodiment the phase rotation circuit 24 performsthe phase rotation processing in decreasing order of phase rotationalangle. Consequently, the complex baseband signal point can be approachedto the reference phase point by a relatively small number of repetitiontimes. This obviates the need for a large number of repetitivecalculations, making phase detection within a short time periodfeasible. Also, the detection system is independent of the amplitudevalue of the complex baseband signal. Consequently, an accurate phasedetection can be performed even in processing a signal, such as areceived signal modulated by a π/4 shift DQPSK system, which changes itsamplitude level in accordance with the phase position.

Other embodiments of the phase detection apparatus according to thepresent invention will be described below. In the following explanationof the other embodiments, the same reference numerals as in the firstembodiment denote the same parts, and a detailed description thereofwill be omitted.

In the first embodiment the reference phase of the comparator 26 isfixed to 0°. In the second embodiment, the reference phase is variableand is set in accordance with the position of the signal point of aninput sample. This allows a phase angle detection with a smaller numberof phase rotational angles than in the first embodiment. Theconfiguration of the second embodiment is the same as the block diagram,FIG. 1, of the first embodiment except that output sample data from aquadrature detection circuit 13 is also supplied to a control circuit 29and the control circuit 29 supplies the reference phase to thecomparator 26 although the fixed value storage circuit 27 is omitted.Therefore, the configuration of the second embodiment is omitted fromthe drawings. Note that as shown in FIG. 5, data in a sin/cos data table25 is slightly different from that in the first embodiment. That is, sindata and cos data representing a rotational angle of 180°/2^(n) (n=1 to7), i.e., seven rotational angles of 90°, 45°, 22.5°, 11.3°, 5.6°, 2.8°,and 1.4°, are stored in a one-to-one correspondence with addresses 1 to7.

FIG. 6 is a flow chart showing the operation of the second embodiment,in which the same steps as in FIG. 3 are not shown.

The second embodiment is identical with the first embodiment from step#10 to step #18 in FIG. 3. In the second embodiment, after step #18steps #52 and #54 are executed and then phase rotation processing instep #20 is executed. In step #52, the control circuit 29 determines thequadrant in which an input sample point A is located. This determinationcan be readily accomplished using the combination of the signs of I andQ components. As illustrated in FIG. 7, in this embodiment both the Iand Q components of the sample point A are negative, so the controlcircuit 29 can determine that the sample point A exists in the thirdquadrant. In step #54, the control circuit 29 sets 90°×(j-1), where j isthe quadrant, as the reference phase of the comparator 26. In the caseof the third quadrant, 180° is set as the reference angle.

Thereafter, as in the first embodiment, the phase rotation processing isperformed in step #20, and in step #22 the signal points before andafter the phase rotation are latched by second and first latch circuits22 and 21, respectively. In step #54, the control circuit 29 determineswhether a parameter i has reached 7. The subsequent operation isidentical with that in the first embodiment.

The operation of the second embodiment will be described in more detailbelow with reference to FIG. 7. Since the sample point of a digitalcomplex baseband signal is the point A in the third quadrant, thereference angle is 180°. The sample point A is first rotated by 90° in aclockwise direction to move to a point B by the phase rotation circuit24. Since the phase of the point B lags behind (the phase is rotated toomuch) the reference phase point (180°), the control circuit writes data"0" in a storage circuit 28.

Phase rotation processing for the second time is performed for thesignal point A before the current phase rotation. The phase rotationcircuit 24 rotates the phase of the signal point A by 45°. Thephase-rotated signal point is a point C in FIG. 7. Since the phase ofthe signal point C leads the reference phase angle 180°, data "1" isstored in the storage circuit 28.

The signal point C leads the reference phase point, and so the phaserotation processing for the third time is performed for the signal pointC. The signal point C is rotated by 22.5° in a clockwise direction.Assume the rotated signal point C agrees with the reference point(180°). In this case data "1" is stored in the storage circuit 28.

Thereafter, the control circuit 29 reads out data "011" from the storagecircuit 28 and supplies 247.5°, which is the sum of a phase (67.5°)represented by the readout data and the reference phase (180°), to acircuit (not shown) as phase detection data.

When the operation is completed, the control circuit 29 reads out thedata "011" stored in the storage circuit 28 and supplies data, which isthe sum of a phase represented by the readout data and the referencephase, to a circuit (not shown) as phase detection data. Note that "011"represents 3 in decimal notation and corresponds to 180°×3/8=67.5° whena phase of 0 to 180° is represented by three bits. Accordingly, thecontrol circuit 29 detects that the phase of the sample A is 247.5°.

In addition to achieving the same effect as in the first embodiment, thesecond embodiment can perform phase detection by rotating the phase onlythree times, which is one less than four times in the first embodiment.This results in a shorter detection time than in the first embodiment.

FIG. 8 is a block diagram of the third embodiment. In each of the aboveembodiments, the phase rotating direction is fixed. Therefore, if thephase is rotated too much, a signal point before the rotation is againrotated; if the rotation is insufficient, the rotated signal point isfurther rotated. Accordingly, two latch circuits are necessary to holdthe signal points before and after the rotation. In this thirdembodiment two latch circuits are unnecessary because the rotatingdirection is selectable. That is, an output from a quadrature detectioncircuit 13 is supplied to a phase rotation circuit 64 via a latchcircuit 62. An output from the phase rotation circuit 64 is fed back tothe latch circuit 62. Although a reference phase of a comparator 26 canbe either fixed or variable, in this embodiment the reference phase isfixed as in the first embodiment. Accordingly, the contents of a sin/cosdata table 25 are the same as those shown in FIG. 2. A control circuit29 controls the rotating direction of the phase rotation circuit 64 inaccordance with the comparison result from the comparator 26.

The operation of the third embodiment will be described below withreference to FIG. 9.

When the operation is started, the control circuit 29 performsinitialization as shown in step #70, i.e., sets 0 in a parameter i whichrepresents the number of rotations.

When A/D converters 18I and 18Q output digital complex baseband signalsof one sample, the data of one sample is latched by the latch circuit 62in step #72.

In step #74, the control circuit 29 sets the phase rotating direction inthe clockwise direction.

In step #76, the control circuit 29 increments the parameter i by 1.

In step #78, the control circuit 29 supplies the parameter i as anaddress to the sin/cos data table 25, reads out sin data and cos datastored in that address, and supplies the readout data to the phaserotation circuit 64. That is, the control circuit 29 first designatesaddress 1 and reads out sin data and cos data corresponding to thelargest phase rotational angle, i.e., 180°.

Assuming an input to the phase rotation circuit 64 is I+jQ, a signalI'+jQ' after the rotation is represented as follows in accordance withthe rotating direction. In the case of the clockwise direction:

    I'=I·cos θ-Q·sin θ

    Q'=Q·cos θ+I·sin θ

In the case of the counterclockwise direction:

    I'=I·cos θ+Q·sin θ

    Q'=Q·cos θ-I·sin θ

In step #80, the phase rotation circuit 64 performs a phase shiftoperation by which the sample point of the digital complex basebandsignal held in the latch circuit 62 is rotated clockwise.

In step #82, the control circuit 29 accumulates the rotational angles.

In step #84, the control circuit 29 causes the latch circuit 62 to latchthe rotated sample point.

In step #86, the control circuit 29 determines whether the parameter ihas reached 8. If YES in step #86, the control circuit 29 terminates theoperation because the phase rotation circuit 64 has completed therotation processing for all of the rotational angles stored in thesin/cos data table 25. If NO in step #86, in step #88 the comparator 26determines whether the rotated signal point agrees with a referencepoint having the reference phase stored in a fixed value storage circuit27. If YES in step #88, the control circuit 29 ends the operation.

If NO in step #88, in the step #90 the control circuit 29 determineswhether the rotated signal point leads the reference phase point. If YESin step #90, in step #92 the control circuit 29 sets the rotatingdirection in the clockwise direction, and the flow returns to step #76to repeat the above operation by incrementing the parameter i by 1. Thatis, the rotated signal point is further rotated clockwise by one-half ofthe immediately preceding rotational angle. If NO in step #90, in step#94 the control circuit 29 sets the rotating direction in thecounterclockwise direction, and the flow returns to step #76 to repeatthe above operation by incrementing the parameter i by 1. That is, therotated signal point is rotated counterclockwise by one-half of theimmediately preceding rotational angle. Note that if the rotatingdirection is the counterclockwise direction, the rotational anglesassigned with negative sign are accumulated; i.e., the rotational anglesare subtractively accumulated.

A practical example of the operation of this embodiment will bedescribed below with reference to FIG. 10. Assume, for example, that thesample point of the digital complex baseband signal is a point A in FIG.10. The sample point A is first rotated by 180° in a clockwise directionto move to a point B by the phase rotation circuit 64 (step #80).Accordingly, 180° is set as an initial value of the accumulated angle.

The comparator 26 compares this phase-rotated signal point B with areference point of phase 0° which is stored in the fixed value storagecircuit 27 (steps #86 and #88).

Since the phase still leads the reference phase after the first phaserotation, the second phase rotation is performed clockwise.Consequently, the phase of the signal point B is rotated by 90° in aclockwise direction. The resulting phase-rotated signal point is a pointC. At this time the accumulated value of the rotational angles is 270°.

The phase-rotated signal point C lags behind the reference phase point(the phase is rotated too much). Therefore, in step #94 the rotatingdirection is set in the counterclockwise direction and the third phaserotation is performed. The signal point C is rotated by 45° in acounterclockwise direction. The consequent accumulated value of therotational angles is 225°.

Since the phase-rotated signal point D leads the reference phase point,the fourth rotation is performed clockwise. The signal point D isrotated by 22.5° in a clockwise direction to become a signal point E.The rotational angle accumulated value is 247.5°.

Since the signal point E agrees with the reference phase point, thecontrol circuit 29 determines that the phase of the sample point A isdetected, and ends the operation. After terminating the operation, thecontrol circuit 29 supplies the rotational angle accumulated value (inthis example 247.5°) to a circuit (not shown) as phase detection data.

As described above, in addition to achieving the same effects as in thefirst and second embodiments, the third embodiment further achieves thefollowing effects. That is, each subsequent phase rotating direction isdetermined in accordance with whether the rotated signal point lagsbehind or leads the reference phase point. Also, the accumulated valueof rotational angles until the rotated signal point agrees with thereference phase point is detected as the phase of the sample point.Accordingly, unlike in the first and second embodiments it isunnecessary to provide two latch circuits and a selector for selectingthem. This further miniaturizes the circuit configuration. Additionally,the processing can be executed in short time periods because processingfor selecting one of two latch circuits also is unnecessary.

The present invention is not limited to the above embodiments but can bepracticed in the form of various modifications. For example, in theabove embodiments the phase rotational angle is sequentially reduced byone-half. However, the phase rotational angle need not be reduced byone-half but can be reduced by, e.g., 1/3. Also, the practical values ofthe rotational angle are merely examples, so angles smaller than 1.4°can be set in the table 25 in order to further improve the accuracy.Although the clockwise direction is used as the basic direction of thephase rotating direction, rotation can be done counterclockwise in thefirst embodiment. In this case the selector 23 needs to select theopposite one of the first and second latch circuits to the one selectedin the first embodiment, in accordance with whether the phase of asignal point leads or lags behind the reference phase. Furthermore, thereference phase point is fixed in the third embodiment, but it is alsopossible to set the reference phase point in accordance with theposition of the sample point as in the second embodiment. Also, therotated signal point is compared with the reference phase point, and, ifthe two points do not agree, the rotated signal point is again rotatedby decreasing the rotational angle. However, if the two points do notagree, the signal point before the rotation can be again rotated bychanging the rotational angle, without using the latch for holding therotated signal point. Additionally, the circuit configuration and thecontrol procedure of the phase detection apparatus and the contents ofthe control also can be modified without departing from the gist of thepresent invention. That is, the above embodiments have been described bytaking a phase detection apparatus using a combination of hardwarecircuits as an example. However, these embodiments can also beconstituted such that phase detection is performed using software byphase rotation control by using a program logic device such as a digitalsignal processor (DSP). With the use of the DSP it is possible toperform phase detection by a relatively short process procedure andcalculation. Accordingly, phase detection can be accomplished withoutusing any large-scale phase detection apparatus within relatively shorttime periods.

Industrial Applicability

As has been described in detail above, the phase detection apparatus ofthe present invention comprises phase rotating means for rotating thephase of an input signal point by a predetermined angle, rotationalangle setting means for supplying a plurality of rotational angles indecreasing order to the phase rotating means, phase comparing means fordetermining whether the signal point rotated by the phase rotating meansagrees with a reference phase point within a predetermined error range,control means for sequentially rotating the phase of the input signalpoint by plurality of the rotational angles until the phase comparingmeans detects the agreement, or, even if the phase comparing means doesnot detect the agreement, until the rotational angle setting meanssupplies all of the rotational angles to the phase rotating means, andphase detecting means for detecting the phase of the input signal pointfrom a sum of the phase rotational angles from the phase rotating means.

According to the phase detection apparatus of the present invention,therefore, phase detection can be performed without using anylarge-capacity memory, so the circuit scale can be decreased compared tothe case where an arc-tangent ROM is used. Consequently, it is possibleto decrease the size and weight of, e.g., a mobile radio communicationapparatus.

Also, since the phase rotation is done in decreasing order of angle, thephase of an input signal can be made agree with the reference phase by arelatively small number of repetition times. This obviates the need fora large number of repetitive calculations, making phase detection withina short time feasible.

Furthermore, the detection system is independent of the amplitude valueof an input signal. Accordingly, an accurate phase detection can beperformed even in processing a signal, such as a received signalmodulated by a π/4 shift DQPSK system, which changes its amplitude levelin accordance with the phase position.

I claim:
 1. A phase detection apparatus comprising:phase rotating means for rotating phases of signal points including a sample signal point; rotational angle setting means for supplying a plurality of rotational angles in decreasing order to said phase rotating means; phase comparing means for determining whether the phases of the signal points rotated by said phase rotating means agree with a reference phase point within a predetermined error range; control means for selectively supplying to said phase rotating means one of signal points before and after an immediately preceding phase rotation to cause said phase rotating means to perform the phase rotation processing by the rotational angle set by said rotational angle setting means, until said phase comparing means detects the agreement, or, even if said phase comparing means does not detect the agreement, until said rotational angle setting means supplies all of the rotational angles to said phase rotating means, and for outputting data indicating the phase of the sample signal point based on a sum of the phase rotational angles.
 2. A phase detection apparatus according to claim 1, wherein said rotational angle setting means comprises a table for storing sine values and cosine values of the rotational angles.
 3. A phase detection apparatus according to claim 1, wherein said rotational angle setting means supplies to said phase rotating means a rotational angle of 360°/2^(n) (n=1, 2, . . . ), if the reference phase point is 0°.
 4. A phase detection apparatus according to claim 1, whereinsaid phase rotating means comprises means for rotating the phases of the signal points in a clockwise direction, and said control means supplies the rotated signal point to said phase rotating means if the phase of the rotated signal point leads the reference phase point in the counterclockwise direction, and supplies the unrotated signal point to said phase rotating means if the phase of the rotated signal point lags behind the reference phase point in the counterclockwise direction.
 5. A phase detection apparatus according to claim 1, whereinsaid phase rotating means comprises means for rotating the phases of the signal points in a counterclockwise direction, and said control means supplies the unrotated signal point to said phase rotating means if the phase of the rotated signal point leads the reference phase point in the counterclockwise direction, and supplies the rotated signal point to said phase rotating means if the phase of the rotated signal point lags behind the reference phase point in the counterclockwise direction.
 6. A phase detection apparatus comprising:phase rotating means for rotating phases of signal points including a sample signal point; phase comparing means for determining whether the phases of the signal points rotated by said phase rotating means agree with a predetermined phase point; and control means for adjusting the rotational angle of said phase rotating means in accordance with the determination result by said phase comparing means so that said phase comparing means detects the agreement, and for outputting data indicating the phase of the sample signal point on the basis of the rotational angle of said phase rotating means, wherein said control means comprises setting means for sequentially setting rotational angles which decrease step by step in said phase rotating means, and said phase rotating means comprises holding means for holding a rotated signal point, and means for rotating the rotated signal point, held by said holding means, by the rotational angle set by said setting means.
 7. A phase detection apparatus according to claim 6, wherein said control means comprises a table for storing sine values and cosine values of the rotational angles.
 8. A phase detection apparatus according to claim 7, wherein said control means comprises a table for storing sine values and cosine values of a rotational angle of 360°/2^(n) (n=1, 2, . . . ), if the predetermined phase point is 0°.
 9. A phase detection apparatus comprising:phase rotating means for rotating phases of signal points including a sample signal point; phase comparing means for determining whether the phases of the signal points rotated by said phase rotating means agree with a predetermined phase point; and control means for adjusting the rotational angle of said phase rotating means in accordance with the determination result by said phase comparing means so that said phase comparing means detects the agreement, and for outputting data indicating the phase of the sample signal point on the basis of the rotational angle of said phase rotating mean, wherein said control means comprises setting means for sequentially setting rotational angles which decrease step by step in said phase rotating means, and said phase rotating means comprises first holding means for holding a rotated signal point, second holding means for holding an unrotated signal point, and means for rotating the signal point held in one of said first and second holding means in a predetermined direction by the rotational angle set by said setting means, in accordance with whether the phase of the rotated signal point leads or lags behind the predetermined phase point.
 10. A phase detection apparatus according to claim 9, wherein said control means comprises a table for storing sine values and cosine values of the rotational angles.
 11. A phase detection apparatus according to claim 10, wherein said control means comprises a table for storing sine values and cosine values of a rotational angle of 360°/2^(n) (n=1, 2, . . . ), if the predetermined phase point is 0°.
 12. A phase detection apparatus comprising:phase rotating means for rotating phases of signal points including a sample signal point; phase comparing means for determining whether the phases of the signal points rotated by said phase rotating means agree with a predetermined phase point; and control means for adjusting the rotational angle of said phase rotating means in accordance with the determination result by said phase comparing means so that said phase comparing means detects the agreement, and for outputting data indicating the phase of the sample signal point on the basis of the rotational angle of said phase rotating means, wherein said control means comprises setting means for sequentially setting rotational angles which decrease step by step in said phase rotating means, and said phase rotating means comprises holding means for holding a rotated signal point, and means for rotating the signal point held in said holding means in a predetermined direction by the rotational angle set by said setting means, in accordance with whether the phase of the rotated signal point leads or lags behind the predetermined phase point.
 13. A phase detection apparatus according to claim 12, wherein said control means comprises a table for storing sine values and cosine values of the rotational angles.
 14. A phase detection apparatus according to claim 13, wherein said control means comprises a table for storing sine values and cosine values of a rotational angle of 360°/2^(n) (n=1, 2, . . . ), if the predetermined phase point is 0°.
 15. A phase detection apparatus comprising:phase rotating means for rotating phases of signal points including a sample signal point; phase comparing means for determining whether the phases of the signal points rotated by said phase rotating means agree with a predetermined phase point; and control means for adjusting the rotational angle of said phase rotating means in accordance with the determination result by said phase comparing means so that said phase comparing means detects the agreement, and for outputting data indicating the phase of the sample signal point on the basis of the rotational angle of said phase rotating means, wherein said phase rotating means comprises means for rotating the phases of the signal points in a clockwise direction, and said control means supplies a rotated signal point to said phase rotating means if the phase of the rotated signal point leads the predetermined phase point in the counterclockwise direction, and supplies an unrotated signal point to said phase rotating means if the phase of the rotated signal point lags behind the predetermined phase point in the counterclockwise direction.
 16. A phase detection apparatus comprising:phase rotating means for rotating phases of signal points including a sample signal point; phase comparing means for determining whether the phases of the signal points rotated by said phase rotating means agree with a predetermined phase point; and control means for adjusting the rotational angle of said phase rotating means in accordance with the determination result by said phase comparing means so that said phase comparing means detects the agreement, and for outputting data indicating the phase of the sample signal point on the basis of the rotational angle of said phase rotating means, wherein said phase rotating means comprises means comprises means for rotating the phases of the signal points in a clockwise direction, and said control means supplies an unrotated signal point to said phase rotating means if the phase of a rotated signal point leads the predetermined phase point in the counterclockwise direction, and supplies the rotated signal point to said phase rotating means if the phase of the rotated signal point lags behind the predetermined phase point in the counterclockwise direction.
 17. A phase detection apparatus comprising:determining means for determining a quadrant in a complex plane in which a sample signal point is located; phase rotating means for rotating phases of signal points including the sample signal point; phase comparing means for determining whether the phases of the signal points rotated by said phase rotating means agree with a predetermined phase point set in accordance with the quadrant determined by said determining means; and control means for adjusting the rotational angle of said phase rotating means in accordance with the determination result from said phase comparing means so that said phase comparing means detects the agreement, and for outputting data indicating the phase of the sample signal point on the basis of the rotational angle of said phase rotating means and the predetermined phase point.
 18. A phase detection apparatus according to claim 17, whereinsaid control means comprises setting means for sequentially setting rotational angles which decrease step by step in said phase rotating means, and said phase rotating means comprises holding means for holding a rotated signal point, and means for rotating the rotated signal point, held by said holding means, by the rotational angle set by said setting means.
 19. A phase detection apparatus according to claim 18, wherein said control means comprises a table for storing sine values and cosine values of the rotational angles.
 20. A phase detection apparatus according to claim 19, wherein said control means comprises a table for storing sine values and cosine values of a rotational angle of 360°/2^(n) (n=1, 2, . . . ), if the predetermined phase point is 0°.
 21. A phase detection apparatus according to claim 17, whereinsaid control means comprises setting means for sequentially setting rotational angles which decrease step by step in said phase rotating means, and said phase rotating means comprises first holding means for holding a rotated signal point, second holding means for holding an unrotated signal point, and means for rotating the signal point held in one of said first and second holding means in a predetermined direction by the rotational angle set by said setting means, in accordance with whether the rotated signal point leads or lags behind the predetermined phase point.
 22. A phase detection apparatus according to claim 21, wherein said control means comprises a table for storing sine values and cosine values of the rotational angles.
 23. A phase detection apparatus according to claim 22, wherein said control means comprises a table for storing sine values and cosine values of a rotational angle of 360°/2^(n) (n=1, 2, . . . ), if the predetermined phase point is 0°.
 24. A phase detection apparatus according to claim 17, whereinsaid means comprises setting means for sequentially setting rotational angles which decrease step by step in said phase rotating means, and said phase rotating means comprises holding means for holding a rotated signal point, and means for rotating the signal point held in said holding means in a predetermined direction by the rotational angle set by said setting means, in accordance with whether the rotated signal point leads or lags behind the predetermined phase point.
 25. A phase detection apparatus according to claim 24, wherein said control means comprises a table for storing sine values and cosine values of the rotational angles.
 26. A phase detection apparatus according to claim 25, wherein said control means comprises a table for storing sine values and cosine values of a rotational angle of 360°/2^(n) (n=1, 2, . . . ), if the predetermined phase point is 0°.
 27. A phase detection apparatus according to claim 17, whereinsaid phase rotating means comprises means for rotating the phases of the signal points in a clockwise direction, and said control means supplies a rotated signal point to said phase rotating means if the phase of the rotated signal point leads the predetermined phase point in the counterclockwise direction, and supplies an unrotated signal point to said phase rotating means if the phase of the rotated signal point lags behind the predetermined phase point in the counterclockwise direction.
 28. A phase detection apparatus according to claim 17, whereinsaid phase rotating means comprises means for rotating the phases of the signal points in a counterclockwise direction, and said control means supplies an unrotated signal point to said phase rotating means if the phase of the rotated signal point leads the predetermined phase point in the counterclockwise direction, and supplies a rotated signal point to said phase rotating means if the phase of the rotated signal point lags behind the predetermined phase point in the counterclockwise direction.
 29. A phase detector comprising:a table containing rotational angle data for a plurality of rotational angles; a phase rotator; and a controller which is configured to determine phase by using the rotational angle data to control said phase rotator such that the respective phases of signals supplied to said phase rotator are rotated relative to a reference phase, wherein said controller uses the rotational angle data to define a series of rotating processes by said phase rotator, each rotating process corresponding to one of the plurality of rotational angles; a first storage location for storing phase data corresponding to the phase of one of said signals after a respective rotating process; a second storage location for storing phase angle data corresponding to the phase of said one of said signals before the respective rotating process; and a selector responsive to a selecting signal from said controller to select an output of one of said first and second storage locations for supplying the selected output to said phase rotator for a rotating process which follows the respective rotating process.
 30. A phase detector according to claim 29, wherein each successive rotating process in the series corresponds to a smaller rotational angle than a preceding rotating process in the series.
 31. A phase detector according to claim 29, whereinsaid phase rotator rotates the respective phases of said signals in a clockwise direction, the selecting signal selects the output of said first storage location if the phase of said one of said signals after the respective rotating operation leads the reference phase in a counterclockwise direction, and the selecting signal selects the output of said second storage location if the phase of said one of said signals after the respective rotating operation lags the reference phase in the counterclockwise direction.
 32. A phase detector according to claim 29, whereinsaid phase rotator rotates the respective phases of said signals in a counterclockwise direction, the selecting signal selects the output of said second storage location if the phase of said one of said signals after the respective rotating operation leads the reference phase in a counterclockwise direction, and the selecting signal selects the output of said first storage location if the phase of said one of said signals after the respective rotating operation lags the reference phase in the counterclockwise direction.
 33. A phase detector according to claim 29, wherein the selecting signal selects the output of one of said first and second storage locations based on whether the phase angle of said one of said signals leads or lags the reference phase after the respective rotating operation.
 34. A phase detector according to claim 29, wherein the reference phase is a constant reference phase.
 35. A phase detector according to claim 34, further comprising:a storage location for storing the constant reference phase.
 36. A phase detector according to claim 29, wherein the reference phase is a variable reference phase.
 37. A phase detector according to claim 36, wherein the variable reference phase is determined in accordance with a quadrant in a complex plane in which one of said signals is located.
 38. A phase detector according to claim 29, wherein the rotational angle data comprises sine and cosine data for the plurality of rotational angles.
 39. A phase detector according to claim 29, wherein said controller controls said phase rotator such that the respective phases of said signals are rotated until the phase of one of said signals is rotated to within a predetermined range around the reference phase or until all of the rotational angles in said table have been used.
 40. A phase detector according to claim 39, further comprising:a comparator for comparing the phase of the signals rotated by said phase detector and the reference phase.
 41. A phase detector according to claim 29, wherein said phase rotator rotates the respective phases of said signals in only one of a clockwise and a counterclockwise direction.
 42. A phase detector according to claim 29, wherein said phase rotator is responsive to a rotation control signal from said controller for rotating the respective phases of said signals in either one of a clockwise and a counterclockwise direction.
 43. A phase detector according to claim 29, wherein said controller determines phase based on an amount of rotation of said signals by said phase rotator. 